The present invention relates to the fabrication of hollow parts of revolution by three-dimensional weaving.
Woven parts of this type act as reinforcements in the fabrication of cylindrical, conical or cylindro-conical hollow bodies obtained by impregnation with a suitable binder followed by machining to the desired precise dimensions of the hollow bodies. Such hollow bodies are employed in particular in the aeronautical field for ballistic objects or rockets such as nozzles, thermal screens or propeller bases. More generally, this type of part can be used in industry whenever high standards are required as concerns mechanical stresses, thermal insulation or high impact and ablation resistance.
Various methods are known for producing hollow cylinders or hollow parts of revolution.
U.S. Pat. No. 3,904,464 discloses a method for producing a hollow body of revolution. It comprises forming, on a specialized tool having the inner shape of the part, a porcupine of radial picots of fibres and polymerized resin. Threads pre-impregnated with resin are wound inside the picots which define passages. A polymerization and then a machining are then carried out. In order to improve the mechanical and thermal properties of the material, the operation may be repeated. This method has drawbacks: the reinforcement is long and complicated to make up and the fabricating operations are numerous and not applicable to all types of fibers.
French Pat. No. 73/14 956 (in the name of the applicant) discloses equipment for producing hollow parts of revolution by a three-dimensional weaving. By means of a perforated head, circumferential and radial threads are simultaneously disposed through a network of longitudinal rods of fibres and polymerized resin. This method permits the production of cylindrical parts, or conical parts with some difficulties, but does not permit the production of parts of complex shapes.
The two embodiments just mentioned have another drawback concerning the quality of the parts obtained, which depends on the fibre content of the latter. This quality depends on an even compacting in the course of fabrication. This compacting is mostly manual and is not effected after the depositing of each layer. The part obtained is heterogeneous if it is thick and this affects its mechanical and thermal properties.
Improvements appear in U.S. Pat. No. 4,183,232 also owned by the applicant. Hollow parts of cylindrical, conical or cylindro-conical shape are produced by introducing between vertically maintained metal rods a helical layer of circumferential and radial threads throughout the height of the part. This method is characterized by the deposit of circumferential threads under low tension and by a radial chain stitching weaving. Throughout the weaving operation, the layers are constantly compacted. The rods are then eliminated and are replaced by threads according to an automatic lacing method described by the applicant in U.S. Pat. No. 4,393,669.
This method permits the production of parts of cylindrical or complex shapes having good mechanical and thermal properties. However, the tooling employed remains relatively complicated and the final shape of the parts is fixed by the weaving operation. An adaptation of the fabricating equipment is required for each type of shape to be obtained.